Re: [PATCH 1/1] OvmfPkg/PlatformInitLib: limit phys-bits to 46.

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 1 Jun 2023 at 10:13, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Thu, 1 Jun 2023 at 09:57, Gerd Hoffmann <kraxel@redhat.com> wrote:
> >
> > Older linux kernels have problems with phys-bits larger than 46,
> > ubuntu 18.04 (kernel 4.15) has been reported to be affected.
> >
> > Reduce phys-bits limit from 47 to 46.
> >
> > Reported-by: Fiona Ebner <f.ebner@proxmox.com>
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>
> Thanks I'll queue this up
>

Merged as #4461

> > ---
> >  OvmfPkg/Library/PlatformInitLib/MemDetect.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/OvmfPkg/Library/PlatformInitLib/MemDetect.c b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
> > index 1102b00ecbf0..662e7e85bbc5 100644
> > --- a/OvmfPkg/Library/PlatformInitLib/MemDetect.c
> > +++ b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
> > @@ -646,16 +646,19 @@ PlatformAddressWidthFromCpuid (
> >      ));
> >
> >    if (Valid) {
> > -    if (PhysBits > 47) {
> > +    if (PhysBits > 46) {
> >        /*
> >         * Avoid 5-level paging altogether for now, which limits
> >         * PhysBits to 48.  Also avoid using address bit 48, due to sign
> >         * extension we can't identity-map these addresses (and lots of
> >         * places in edk2 assume we have everything identity-mapped).
> >         * So the actual limit is 47.
> > +       *
> > +       * Also some older linux kernels apparently have problems handling
> > +       * phys-bits > 46 correctly, so use that as limit.
> >         */
> > -      DEBUG ((DEBUG_INFO, "%a: limit PhysBits to 47 (avoid 5-level paging)\n", __func__));
> > -      PhysBits = 47;
> > +      DEBUG ((DEBUG_INFO, "%a: limit PhysBits to 46 (avoid 5-level paging)\n", __func__));
> > +      PhysBits = 46;
> >      }
> >
> >      if (!Page1GSupport && (PhysBits > 40)) {
> > --
> > 2.40.1
> >